Streptococcus suisis a worldwide pathogen that impacts swine industry, causing severe clinical signs in postweaning piglets, including meningitis and arthritis. Biofilm formation is a major virulence mechanism inS. suis, enhancing its persistence and resistance. Here, we assessed thein vitrobiofilm formation of 240S. suisisolates from Spanish swine farms and evaluated the effects of serovars (SVs) and coinfections with other porcine respiratory disease complex (PRDC) pathogens. Our study revealed significant heterogeneity in biofilm formation amongS. suisSVs. Notably, SV2 exhibited the lowest biofilm formation, contrasting with the high biofilm-forming capacities of SV1, SV7, and SV9. Virulence factorsepf,mrp, andslywere associated (p< 0.05) with reduced biofilm formation. Other PRDC pathogens, includingActinobacillus pleuropneumoniae,Glaesserella parasuis, andPasteurella multocida, formed biofilms, though generally less robust than those ofS. suis(except for SV2), contrasting the high biofilm formation ofStaphylococcus hyicus. Coinfections demonstrated enhanced biofilm formation in mixed cultures ofS. suis, particularly withP. multocida. Other coinfections revealed variable results in pathogen interactions, suggesting the potential of biofilms for increased persistence and pathogenicity in coinfections. In conclusion, this study underscores the importance of serovar-specific differences in biofilm formation amongS. suisisolates, with significant implications for pathogenicity and persistence. The heterogeneous biofilm formation observed in coinfections with other PRDC pathogens reveals a complex interplay that could exacerbate disease severity. These findings provide a foundation for further research on biofilm mechanisms to mitigate the impact of PRDC in the swine industry.
